The peripheral olfactory neuroepithelium is able to regenerate after injury; however the signals that initiate the complex cascade leading to increased cell proliferation and neurogenesis are poorly understood. We will examine ATP as an important local trophic factor in injury-evoked olfactory neuron regeneration. We hypothesize that noxious insult to the olfactory epithelium triggers an extracellular ATP-induced signaling cascade that initiates regeneration of the neuroepithelium. We base this hypothesis on the observation that (1) cell damage, iysis and also regulated processes will release ATP into the extracellular milieu and (2) activation of purinergic receptors induces synthesis and/or release of neurotrophic factors, mitogenesis, and differentiation in the CNS. Thus, ATP released by acutely injured cells could stimulate localized regeneration due to the mitogenic and growth-promoting effects of purinergic receptor activation. Growth promotion can be mediated by G protein coupled purinergic receptors located on sustentacular support cells and basal stem cells, which, like other growth factor receptors, induce a cascade of intracellular events that trigger cell proliferation. Our specific aims are to (1) Determine if noxious and physiological stimuli evoke release of ATP in the OE. We will identify toxicological and physiological stimuli, pathways of release and sources of ATP using bioluminescence assays and confocal microscopy. (2) Determine if extracellular ATP and purinergic receptor activation elicits the release of neurotrophic factors. We will measure ATP-induced increases in membrane capacitance as an indication of exocytosis, vesicular release of ATP, and release of neurotrophic factors using electrophysiology, confocal microscopy and immunocytochemistry. (3) Determine if extracellular ATP and activation of purinergic receptors elicits proliferation. We will determine if ATP is sufficient to initiate proliferation or acts synergistically to initiate proliferation in the uninjured olfactory epithelium, and/or promotes injury-evoked proliferation using immunohistochemistry and in vitro and in vivo assays. This data will clearly have implications for the pharmacological modulation of proliferation. Agents that modify the effects of purinergics and purinergic receptors are readily available and could therapeutically modulate cell proliferation and differentiation, in the olfactory system and in the CNS.